This invention relates to photoelectric position measuring systems for measuring the relative position of two objects, of the type which utilize a diffraction grating to generate at least two diffracted component beams.
West German DE-OS No. 33 16 144 and Japanese unexamined patent specification JP-OS No. 59-164 914 describe two measuring systems of the general type described above. In such systems the diffraction grating defines the reference magnitude. A diffraction grating is made up of very thin grating lines that lie closely adjacent to one another, for example on a glass or metal plate. Such gratings may be formed by mechanical processing techniques, by photolithographic techniques, or by electron beam lithography. Such measuring systems further include a light source that emits monochromatic light, two reflector mirrors, and a detector on the side of the diffraction grating opposite the light source. Diffracted beams from the grating are brought into interference, and the detector is responsive to the resulting interference pattern. The light beam emitted from the light source is diffracted by the diffraction grating and passed. If one assumes that the diffraction grating is moved with respect to another part of the optical system (such as the light source and the reflector mirrors), then the output signal of the detector in response to the interference pattern moves through two periods when the diffraction grating moves through one period.
In another arrangement the light beam emitted from the light source is diffracted by the diffraction grating, and light beams of the same order with different signs (+or -) overlap and interfere with one another. For example a semipermeable mirror may be provided before the light enters the detector. As before, relative movement occurs between the diffraction grating and another part of the optical system. As explained above, the interference pattern moves through two periods while the diffraction grating moves through one period.
One important problem in the design of such measuring systems is to accommodate the required optical system in a small space. The optical system can easily become extensive, so that a relatively large physical layout is required.
U.S. patent application Ser. No. 07/077,190 filed on July 24, 1987 discloses a measuring system which is simple in construction and which largely eliminates disturbances caused by environmental influences, thereby providing dependable operation. The advantages of this measuring system are that it provides a compact construction in a system with high integration capacity and with excellent security with respect to environmental influences.